supersonic air-jet

bogart · March 22, 2010, 04:36

Dear All,
I am trying to model a fully expanded (ambient) supersonic air-jet out of a nozzle using a 2d-axisymmetric geometry. The nozzle geometry is not included in the model, only the nozzle outlet is introduced as a mass-inlet boundary condition. I am using the pressure-based coupled solver. The operating pressure is set at 101 kPa, atmospheric. Since I want total expansion at the nozzle outlet, I specify the supersonic gauge pressure as 0 at the nozzle outlet (mass-inlet BC). In the solution I obtain however, the FLUENT solver calculates the static pressure at nozzle outlet as 54 kPa. So, I cannot get a fully expanded air-jet. Is there anyone who knows what I might be doing wrong, or how to control the nozzle exit pressure?
The velocity at the nozzle outlet is above Ma 2.5. I have quite a fine mesh and a stably converged solution.

Your help is much appreciated.
Regards,

bogart · March 25, 2010, 05:31

a small update from my side: i kept altering the mass-inlet boundary by small increments, leading to significant increase in total. as a result, the static pressure at the nozzle outlet increases, whereas the increase in velocity isn't that significant. seems weird to me. especially since I set the supersonic gauge pressure to a definite value.

i need to control the static pressure at nozzle outlet. anyone who knows what I might be doing wrong?

March 22, 2010, 04:36	supersonic air-jet	#1
bogart New Member Join Date: Mar 2010 Posts: 4 Rep Power: 16	Dear All, I am trying to model a fully expanded (ambient) supersonic air-jet out of a nozzle using a 2d-axisymmetric geometry. The nozzle geometry is not included in the model, only the nozzle outlet is introduced as a mass-inlet boundary condition. I am using the pressure-based coupled solver. The operating pressure is set at 101 kPa, atmospheric. Since I want total expansion at the nozzle outlet, I specify the supersonic gauge pressure as 0 at the nozzle outlet (mass-inlet BC). In the solution I obtain however, the FLUENT solver calculates the static pressure at nozzle outlet as 54 kPa. So, I cannot get a fully expanded air-jet. Is there anyone who knows what I might be doing wrong, or how to control the nozzle exit pressure? The velocity at the nozzle outlet is above Ma 2.5. I have quite a fine mesh and a stably converged solution. Your help is much appreciated. Regards,

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March 25, 2010, 05:31		#2
bogart New Member Join Date: Mar 2010 Posts: 4 Rep Power: 16	a small update from my side: i kept altering the mass-inlet boundary by small increments, leading to significant increase in total. as a result, the static pressure at the nozzle outlet increases, whereas the increase in velocity isn't that significant. seems weird to me. especially since I set the supersonic gauge pressure to a definite value. i need to control the static pressure at nozzle outlet. anyone who knows what I might be doing wrong?